AES67 vs. ST2110-30: What's the Difference?
In the IP-based transformation of broadcasting audio systems, AES67 and SMPTE ST 2110-30 are two critically important standards. Although they share a highly common technological foundation, their design objectives and application scenarios exhibit distinct differences. This article will elaborate on their differences to help system designers and operational personnel better understand and select between them.
Positioning and Application Scenarios
AES67: Developed by the Audio Engineering Society, it is a cross-platform interoperability standard designed for pure audio systems. It aims to achieve basic interoperability between different AoIP protocols.
ST2110-30: Part of the SMPTE ST 2110 audiovisual IP-based standard system, it primarily serves integrated audiovisual broadcasting production systems, emphasizing audio synchronization and signal coordination in video environments.
Simply put, AES67 is suitable for standalone audio systems or acts as a “lingua franca” for system interconnection, whereas ST2110-30 is a tailored audio transmission solution for broadcasting IP video systems. Of course, ST2110-30 can also be used in pure audio environments, offering good compatibility.
Common Technical Foundation
Both standards originate from the RAVENNA architecture and share the following core mechanisms:
Use of RTP/UDP for transmitting uncompressed PCM audio;
Reliance on PTPv2 (IEEE 1588-2008) for high-precision clock synchronization;
Support for multicast transmission mode.
Key Differences
1. Audio Stream Format and Channel Count
AES67 supports more flexible packet time and channel count combinations:
Packet Time | Maximum Channels |
|---|---|
1 ms | 10 |
1/3 ms (≈0.333 ms) | 30 |
1/4 ms (0.25 ms) | 40 |
1/8 ms (0.125 ms) | 80 |
ST2110-30 has a simpler structure, divided into three levels:
Level | Packet Time | Maximum Channels |
|---|---|---|
A | 1 ms | 8 |
B | 1/8 ms (0.125 ms) | 8 |
C | 1/8 ms (0.125 ms) | 64 |
The structure of ST2110-30 is more aligned with the common channel counts and low-latency requirements in broadcasting production.
2. “Slave Only” Mode for Clock Synchronization
ST2110-30 requires devices to have a ”Slave Only” option. When enabled, the device will not participate in the PTP master clock election and will always operate as a slave clock, preventing system synchronization failures caused by erroneous clock switching.
AES67 has no such mandatory requirement; devices can freely participate in the master clock election.
3. PTP Domain
AES67 defaults to PTP Domain = 0 (configurable range 0–127);
ST2110 systems comply with ST2059-2, which specifies a default Domain = 127.
To integrate an AES67 device into an ST2110 system, its PTP Domain must be changed to 127. However, some AES67 devices (particularly certain Dante models) do not support modifying the Domain, resulting in an inability to receive ST2110-30 audio streams. This is a common compatibility issue in system integration.
Other Subtle but Notable Differences
ST2110-30 allows devices to use a local clock (baseband clock). In this case, the SDP information will be marked as
a=ts-refclk:localmac=<MAC address>, which some AES67 devices may not recognize as a clock source.ST2110-30 requires that the offset between the RTP clock and the media clock must be zero.
ST2110-30 does not mandate support for RTCP or SIP protocols.
For implementing audio stream redundancy, ST2110-30 recommends adherence to the SMPTE ST 2022-7 standard (seamless protection switching), while AES67 does not specify a redundancy mechanism.